As an aspect of a network including a plurality of nodes, a multi-hop wireless network in which each node equipment is capable of autonomously performing communications has been put into practical use. In the network, each node equipment may autonomously select a route of a packet. That is, each node equipment functions as a router or a switch. Each node equipment may recognize the configuration of a surrounding network by communicating a message etc. with adjacent node equipment. Therefore, in this system, a desired network may be created only by implementing a node equipment in an environment in which the network is to be created without providing management equipment for managing the entire network. Also in this method, a node may be easily added or deleted, thereby flexibly changing the configuration of a network.
Proposed as the technology related to a multi-hop wireless network is a method for allowing each wireless sensor node to sequentially transfer a data packet to a wireless server node (for example, the Japanese Laid-open Patent Publication No. 2005-223497). Also proposed as another related technology is a multi-hop wireless network capable of easily performing monitoring and controlling processes with low power consumption (for example, the Japanese Laid-open Patent Publication No. 2006-222650). Proposed as a further related technology are an equipment and a method capable of efficiently performing flooding communications and performing stable communications (for example, the Japanese Laid-open Patent Publication No. 2009-225172).
In a multi-hop wireless network, when the state or the performance of a node is degraded, there is the possibility that the performance is degraded in a large area in the network. For example, when there occurs the congestion in a certain node, the efficiency of the data transmission becomes lower in the route which passes through the node, and a packet may be discarded depending on a condition. Therefore, it is preferable that a user or a network administrator may quickly detect a node in a poor state.
The method of monitoring the state of each node in a multi-hop wireless network is realized by, for example, the procedure of each node equipment which detects the state (congestion, reception power, etc.) of the local node and transmits the result of the detection to a server computer. In this case, the server computer may collect the state information from all nodes, perform statistical processing etc., and detect a node in a poor state. However, in this method, when the number of nodes is large, the computational complexity of the server computer is serious, and it is necessary to provide a large memory area to store data received from each node. Furthermore, in this method, the traffic for each node which notifies the server computer of the state becomes heavy.
To improve the problem above, for example, a threshold for judgment of the state is set in each node equipment, and only a node equipment whose state is lower than the threshold outputs an alarm message. However, it is difficult to determine a threshold in this method. That is, if the threshold is too high, there is the possibility that a node in a poor state is not detected. On the other hand, when the threshold is too low, an alarm message is output from a large number of nodes, and there is the possibility that a node which is practically and badly degraded is not specified. Therefore, to detect a node in a degraded state with high accuracy, it is preferable that a server computer collects the state information about a multi-hop wireless network.